I suspect that low urban obesity is largely driven by class confounders: very high concentration of SWPLs/Brahmins rather than proles/Vaisyas. Same with Northern Virginia. SWPLs tend to actively care about their health and pride themselves on eating whole foods rather than processed foods, so it's not surprising that they're thinner (probably also somewhat lower genetic load).
Likewise, I don't think most diet/exercise based explanations can explain why obesity has shot up so much more quickly in the past ~20 years. I can maybe buy less hyperpalatable food and more exercise in 1970 then today, but I highly doubt there's been a major shift in the past couple of decades. More food also doesn't jibe with stuff like the China study data from Nanan, where sedentary office workers were consuming ~3600 kcals a day at a baseline weight of 120 pounds (far more kcals/pound then modern Americans), and not getting fat (https://fireinabottle.net/the-curious-case-of-nanan-and-huain/). The one exception is the linoleic acid/seed oil hypothesis, because vegetable consumption has risen monotonically basically everywhere over the past ~20 years. If had to put money on one major driver of obesity, it would be that (don't find Slime Mold's criticisms convincing for a number of reasons), but still low confidence that that's correct.
Protein/nutrient leverage may have something to do with it, but I think that "paleo" diets and related ones (high on meats, eggs, vegetables, and other very nutrient dense foods) would be more successful if that was a major factor. These diets do work pretty well, but not so well that they're a magic bullet, which they should be if protein/nutrient leverage is the major driver of obesity. And then you have things like the rice diet, potato diet, and croissant diet, all of which also work fairly well, when they should be utter garbage if protein/nutrient leverage is a major driver.
As for muscle strength: the obvious question then becomes, "why are we weaker"? Were Americans in 1990 really doing backbreaking labor compared to Americans in 2020? It probably has something to do with the massive generational decline in male testosterone... but nobody knows what's causing that. And as far as I know, T levels have been increasing outside the West, yet India and China are now getting full-force diabesity as well.
Increasing maternal age is an interesting point, one which I hadn't seen yet. Maybe feminism is what's causing the obesity crisis. Lower T in men (thus weaker and fatter), higher T in women (associated with more visceral fat in women), fat acceptance (for those social network effects), fewer homecooked meals, higher maternal age... (but I don't think this is actually true: the Middle East is the world's fattest major region, and certainly not the most feminist, especially not in 1970).
I suspect that low urban obesity is largely driven by class confounders: very high concentration of SWPLs/Brahmins rather than proles/Vaisyas. Same with Northern Virginia. SWPLs tend to actively care about their health and pride themselves on eating whole foods rather than processed foods, so it's not surprising that they're thinner (probably also somewhat lower genetic load).
Likewise, I don't think most diet/exercise based explanations can explain why obesity has shot up so much more quickly in the past ~20 years. I can maybe buy less hyperpalatable food and more exercise in 1970 then today, but I highly doubt there's been a major shift in the past couple of decades. More food also doesn't jibe with stuff like the China study data from Nanan, where sedentary office workers were consuming ~3600 kcals a day at a baseline weight of 120 pounds (far more kcals/pound then modern Americans), and not getting fat (https://fireinabottle.net/the-curious-case-of-nanan-and-huain/). The one exception is the linoleic acid/seed oil hypothesis, because vegetable consumption has risen monotonically basically everywhere over the past ~20 years. If had to put money on one major driver of obesity, it would be that (don't find Slime Mold's criticisms convincing for a number of reasons), but still low confidence that that's correct.
Protein/nutrient leverage may have something to do with it, but I think that "paleo" diets and related ones (high on meats, eggs, vegetables, and other very nutrient dense foods) would be more successful if that was a major factor. These diets do work pretty well, but not so well that they're a magic bullet, which they should be if protein/nutrient leverage is the major driver of obesity. And then you have things like the rice diet, potato diet, and croissant diet, all of which also work fairly well, when they should be utter garbage if protein/nutrient leverage is a major driver.
As for muscle strength: the obvious question then becomes, "why are we weaker"? Were Americans in 1990 really doing backbreaking labor compared to Americans in 2020? It probably has something to do with the massive generational decline in male testosterone... but nobody knows what's causing that. And as far as I know, T levels have been increasing outside the West, yet India and China are now getting full-force diabesity as well.
Increasing maternal age is an interesting point, one which I hadn't seen yet. Maybe feminism is what's causing the obesity crisis. Lower T in men (thus weaker and fatter), higher T in women (associated with more visceral fat in women), fat acceptance (for those social network effects), fewer homecooked meals, higher maternal age... (but I don't think this is actually true: the Middle East is the world's fattest major region, and certainly not the most feminist, especially not in 1970).